Well, if you use a poor card and run a desktop with composite, you'll get a poor desktop or game, because the card cannot manage so much datas.

You need to gave one job, and the card will do its best at it.
Disable composite and get game speed, but 2D desktop, no effect, and the speed of the card in 2D, not 3D. This should gave you the best result.

Or you may enable composite desktop to enable 3D handling of your desktop (that should gave better result than 2D or not, depend on the card, i'm not sure how powerful a 8300 could be) and disable it before running any game.
So for compiz it would be : killall compiz && runyourgame && compiz-start &

I suppose if your game run smooth you've select opengl already no? But it never kill to recheck that.

That's generality, i'm not sure if/how KDE handle composite, but i assume it do. And with the infos you gave, i don't see more to add.

on nvidia-drivers 173 i have laggy desktop 100% of the time and java games(minecraft) runs fine.

on nvidia-drivers 304 Desktop runs smooth 99% of the time and java will run great for a few mins before locking up with lag.

i dont have compiz installed. but the card even being onboard should be able to handle it ok. seems like kde doesnt like the older driver for some reason.
if there some other composite that i can shut off.. kde was compiled on the new driver.. should i re-emerge it on the old driver?